1. Field of the Invention
The present invention relates to an image forming apparatus including an image bearing member and a development device that includes a developer bearing member, which can bear a developer, to visualize an electrostatic image on a surface of the image bearing member using toner borne by the developer bearing member.
2. Description of the Related Art
Recently, in the image forming apparatus such as a copying machine and a printer, it is necessary to rotate the image bearing member, the developer bearing member, and a fixing roller at a high speed in order to respond to high-speed printing that is the needs of a user. However, an amount of heat necessary to fix the toner depends on a kind of a transfer material. Therefore, sometimes image formation is performed while a gap between pieces of paper is widened, when the image formation is performed on the transfer material in which the large amount of heat is necessary to fix the toner. At this point, in one job, it is assumed that the printing is continuously performed to the transfer materials in which the large amount of heat is necessary to fix the toner. When the number of transfer materials passing through a fixing device is decreased per unit time, an electrostatic image absent region between the preceding electrostatic image and the subsequent electrostatic image is widened on the image bearing member. Therefore, the developer bearing member uselessly rotates when the developer bearing member rotates while the electrostatic image absent region moves in a position opposite the developer bearing member. The developer on the developer bearing member is degraded by the rotation of the developer bearing member, which results in degradation of image quality. For example, Japanese Patent Laid-Open No. 2007-264553 discloses an image forming apparatus in which the degradation of the image quality is suppressed. The image forming apparatus disclosed in Japanese Patent Laid-Open No. 2007-264553 includes a unit that computes a coverage rate A of image data to fix a toner ejection time t1 and a unit that computes an integrated toner ejection time (T) each time an image forming process is performed. The image forming apparatus performs a toner refresh process when the integrated value reaches a predetermined value. According to the image forming apparatus disclosed in Japanese Patent Laid-Open No. 2007-264553, even in the high-speed printing, the image quality is maintained to suppress the toner refresh process to the minimum necessary.
However, unfortunately, a down time or a consumed amount of toner that does not directly contribute to the image formation increase in the image forming apparatus of Japanese Patent Laid-Open No. 2007-264553 in which the toner refresh process is performed.
Therefore, Japanese Patent Laid-Open No. 2008-039967 discloses a configuration in which, in order to prevent the developer degradation caused by a long-term operation of the development device, the development sleeve is stopped or slows down in a region corresponding to a gap between the pieces of paper when the image is continuously formed or when an interval (gap between pieces of paper) of a non-image forming region becomes longer than usual.
However, in the configuration of Japanese Patent Laid-Open No. 2008-039967, irrespective of an environment, a rotation speed of the development sleeve slows down or stops without any exception, while the inventor found that the progression of the developer degradation is largely influenced by the environment of the apparatus. Accordingly, in the configuration of Japanese Patent Laid-Open No. 2008-039967, even in the low-temperature environment in which the developer is relatively hardly degraded, a motor of the development sleeve is turned on and off beyond necessity, unfortunately a lifetime and reliability of the motor are reduced.